The use of mechanical stirrers to foam sump oil in refrigeration compressors for noise suppression purposes is old but remains a very viable and popular method of compressor noise attenuation. Typical in this regard are the mechanical stirrers of U.S. Pat. Nos. 2,990,111; 3,480,205; 4,127,994; and 4,545,743. As is noted in U.S. Pat. No. 4,063,853, however, one disadvantage which accompanies the agitation or stirring of the oil in a compressor sump is that contaminants and particles of debris, normally found at the bottom of the oil sump, can be stirred into the oil and can find their way into the bearings of the motor-compressor unit if not otherwise prevented from doing so. This, of course, reduces bearing life in the motor-compressor unit and can lead to a catastrophic failure of it.
Further, it has been specifically recognized that mechanical agitation of compressor sump oil can result in the generation of waves within the sump oil that create a disturbing sloshing noise which emanates from the shell. That is, the very means by which noise suppression is sought to be achieved in some compressors can create a discrete and equally disturbing compressor noise problem. This problem is addressed in U.S. Pat. No. 3,480,205 to Hatten in which a series of baffles are arranged in the oil sump of a compressor to break up such waves to reduce or eliminate the sloshing noise which would otherwise result. The baffles of the Hatten patent are concentric rings disposed around the mechanical stirrer. The bottom of the compressor shell, which is also the bottom of the oil sump therein, is nonetheless fully exposed in Hatten to the stirrer and the turbulence created by it in the oil agitation process.
There exists a need for apparatus in a refrigeration compressor which allows for and promotes the agitation and foaming of sump oil for noise attenuation purposes while preventing the mixing of debris found at the bottom of the oil sump into the compressor oil supply.